In the world of security one of the most important rules is to not open attachments in email if you don’t expect it. Notice I didn’t day know the person. Most spam and email borne viruses use the contact lists of others to send out themselves, hoping you will think it came from someone you know and open it. So when that really cool video, or a cjoupon you must have to save hundreds comes in you email, DON’T DOWNLOAD THAT FILE. Just delete it and check with your friends. If they sent it then they can send it again, if not you saved yourself countless hours of rebuilding your system and sometimes your bank account.